SCIENCE & TECHNOLOGY
 

Our mysterious sun; inside out
Santanu Banerjee
T
he light from the sun takes only eight minutes and 24 seconds to reach the earth thus describing our only day time star to be 8.24 light minutes away from us. The sun — the head of the solar family — emits light over the entire electromagnetic spectrum ranging from the x-rays to the radio waves including the visible region.

Magnetic refrigeration
M
agnets are big-time materials, finding roles in products ranging from motors to medical-imaging systems. Now, a team of engineers’ improvement of a custom-made magnetic material increases the odds that refrigeration will soon join the roster of magnet-based technologies.

YASH PALUNDERSTANDING THE UNIVERSE
WITH PROF YASH PAL

When you observe a pot of water on a gas flame that has been already brought to boil you do not see any steam coming out from the top. But as soon as you switch off the flame the top of the pot is covered by lot of vapour whirling around. Why?

New products & discoveries

  • Mapping the galaxy

  • Mobile do-it-all player

  • "Ageing gene"Top

 




 

Our mysterious sun; inside out
Santanu Banerjee

The light from the sun takes only eight minutes and 24 seconds to reach the earth thus describing our only day time star to be 8.24 light minutes away from us. The sun — the head of the solar family — emits light over the entire electromagnetic spectrum ranging from the x-rays to the radio waves including the visible region. The majority of the solar radiations are in the visible as well as the infrared regions. The photons being the quanta of light bring the information about the sun’s structure and dynamics.

The sun being the closest star is much easier to study compared to others. The next nearest star, Proxima Centuari, is 4.2 light years away and the next to next, Aldebaran is 60 light years away. Sounds amazing? Then hold your breath, our nearest Galaxy is just three million light years away. In this scale, the sun is only two-thirds of a millionth of a light year away from us.

We all know that the sun is massive, almost 0.33 million times heavier than the earth. Yet the mean solar density is only 0.25 times the earth’s mean density. This 4.57 billion years old star takes about 25 earth days at equator to complete one rotation about its own axis. The ingredients of the solar composition are entirely gaseous with hydrogen and helium constituting the lions share. While hydrogen is abundant at the surface (70%), the central core is rich in helium (63%).

The more the hydrogen fuel left, the more is the temperature of the star. From that point of view the sun is a much cooler variant having a surface temperature of 5770 Kelvin. The coolest stars are seen reddish (e.g. the Menkar) while the hottest ones appear blue (e.g. the Alnilam) to the naked eye. Quite interestingly, our sun is also a much smaller variant of stars with a size of only 0.86 million miles diameter. The Supergiant, Alpha Aquarii, is a hefty 95 million miles in diameter. But the biggest of the stars are not necessarily the hottest. The Supergiant, Alnilam, being much smaller (27 million miles) is a blue star while the Alpha Aquarii is a yellow one.

Stunningly, the sun is having an escape velocity of 55.2 times that of the earth, i.e. 618 km/s.

The central core temperature of the sun is estimated to be about 15 million degrees centigrade. The pressure there is 250 billion times the earth atmospheric pressure. That’s why energy production is so difficult in the same process as in the sun, here on earth.

The enormous solar energy results from the well known ‘pp’ chain reaction. Basically, four protons fuse to give one helium nucleus, and release huge energy, carried by the g -ray. In the process the solar mass is being burnt to produce the energy according to the famous equation of Einstein, E=mc2.

Then one question pops up — what is the rate of reduction of solar mass and how many years will the fuel last to keep the sun glowing? Hold on! The solar nuclear furnace consumes five million tons of solar mass per second and still enough materials is available there to continue the reactions for more than a staggering 100 billion years.

According to the standard solar model, sun started its life by contraction of gas composed of mostly hydrogen and helium. The initial composition altered by steady increase of helium through nuclear "burning". Energy generated at the central core transferred outward by radiation, and then by convection further out from the centre. But the enormous number of neutrinos produced and entering the earth atmosphere are extremely non-interactive and hence quite difficult to detect.

The photosphere is the visible surface of the sun that we are most familiar with. Since the sun is a ball of gas, this is not a solid surface but is actually a layer about 100 km thick (very, very thin compared to the 700,000 km radius of the sun). A number of features can be observed in the photosphere viz. the dark sunspots, the bright faculae, and granules.

The chromosphere is an irregular layer above the photosphere where the temperature rises from 6000`B0 C to 20,000`B0 C. The chromosphere is the site of lot of activities as well. The corona is the sun’s outer atmosphere. It is visible during total eclipses of the sun as a pearly white crown surrounding the sun. It displays a variety of features, including streamers, plumes, and loops. These features change from eclipse to eclipse and the overall coronal shape changes with the sunspot cycle.

A wind of charged particles streams off of the sun in all directions at speeds of about 400 km/s. The source of the solar wind is the sun’s hot corona. The temperature of the corona is so high that the sun’s gravity cannot hold on to it. A bubble called Heliosphere is produced in space by the solar wind.

Basic features of the solar anatomy are known to us today but the finer details are yet to be sorted out and it is extremely challenging as we have very few techniques to probe into the sun.

The writer is with Institute of Plasma Research, Gandhinagar
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Magnetic refrigeration

Magnets are big-time materials, finding roles in products ranging from motors to medical-imaging systems. Now, a team of engineers’ improvement of a custom-made magnetic material increases the odds that refrigeration will soon join the roster of magnet-based technologies.

With the goal of making refrigerators and air conditioners more efficient, several groups around the world are developing magnetic-refrigerant materials. A magnetic-cooling system could also be less polluting than current systems because it wouldn’t use environmentally harmful chemicals, such as ammonia or chlorofluorocarbons.

What’s more, the technology requires few moving parts, so it can be simple, silent, and reliable. When a magnetic-refrigerant material is exposed to a magnetic field, the field forces the spins of electrons in the material to align. As a result, the material heats up. Removing the field permits the electrons to relax into less-ordered states, and the material cools down. By cycling the material through these hot and cold states and venting away the heat, the system can generate an overall cooling effect.
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UNDERSTANDING THE UNIVERSE
WITH PROF YASH PAL

When you observe a pot of water on a gas flame that has been already brought to boil you do not see any steam coming out from the top. But as soon as you switch off the flame the top of the pot is covered by lot of vapour whirling around. Why?

Firstly the observation that you do not see any steam over the pot when flame is on and the water is boiling. The reason lies in the fact that hot steam is an invisible gas. You seem to see it when it turns into vapour - when it condenses into a cloud. When the flame is on there is a lot of hot air going up along the sides of the pot and that does not allow the steam to condense and become visible. However, as soon as you turn off the gas burner the upward draft of hot air is stopped and is replaced by cooler air from the sides. This makes the vapour condense and become visible as whirling cloud.

You might test this explanation by doing another experiment, which I did. Instead of boiling water in a pan over a gas flame I boiled it in an electric kettle while keeping its stopper off.

The electric kettle does not get hot on the outside. I found that in this case the steam from the vigorously boiling water did become visible in the form of a cloud even while the kettle was kept on and the water kept on boiling. The cooler air from the side did its work.

A friend drew my attention to another phenomenon that had not come to my attention, but was known to younger people, including my wife.

Soon after you place a shining stainless steel pot half filled with cool water on a gas burner, you notice a thin film of water on the outside, going up to the level of the water inside! This disappears after a while when the water inside becomes quite hot, but where does it come from - surely not from inside the pot?

Then an intelligence dawns and you realise that burning of gas, which after all is a hydrocarbon, produces water along with carbon dioxide The gas contains lot of hydrogen atoms, along with carbon and some other stuff and burning of hydrogen must lead to water. Going up on the side of the pot, some of the vapour condenses on its cool surface.

If a sheep can be cloned then why not a man?

I think it should be possible. Some time in future. Whether one should go into this is another question. Besides ethical questions one should also remember that risks remain and we do not want to have malfunctioning humans produced.

One should remember that human beings stand demeaned if they get multiplied for their physical attributes alone. It might be possible to clone the genetic makeup but the important part of being human is to nurture.

We also do not want to get to value framework in which defective humans would be eliminated the way we eliminate defective animals.

On the other hand there might be much less worries about cloning spare parts such as kidney, liver, even the heart. One can foresee that the rich and old would keep a bank of spare parts for the eventuality that they might need them. This could become quite an industry for the rich and the super rich. I doubt if common people will be able to afford this luxury.

Despite of the tremendous repulsion between positive charges, how can many protons reside in the atomic nucleus?

We know that helium2 (He?) does not exist. In other words we cannot have a nucleus with only two protons. But He3 does exist. The nucleus of He3 has a neutron in addition to two protons. The reason is that there is strong short-range nuclear force between all nucleons — protons and neutrons — alike.

The character of this short-range force, called the strong force, is different from that of the electrical force. Thus inside the nucleus we have two opposing forces — repulsion between positively charged protons and attraction between protons and neutrons. With increasing atomic numbers, the number of neutrons is significantly greater than the number of protons. Thus the abundant form of uranium has a total of 146 neutrons and only 92 protons.
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New products & discoveries

Mapping the galaxy

Gaia spacecraftOne of European Space Agency’s most ambitious current projects has the aim of compiling the most precise map of one thousand million stars in our Galaxy.

Gaia, a spacecraft which will carry two of the most sensitive cameras ever made, is due to be launched in 2010.

It will take five years to detect such a vast quantity of objects, some of which are incredibly faint, and another three years to plot them all in a giant three-dimensional computerised model that shows not only their current position, but their direction of motion, colour and even their composition.

In short, Gaia will produce a completely new view of the galaxy and everything in it. It will produce the ultimate map, a star catalogue that could be used by every other space mission of the future.

Another exciting aspect of this amazing mission is that it could find objects that we did not know existed - until Gaia turns its supersensitive cameras in their direction.

Mobile do-it-all player

MP3 players are small, light and can play music. Computer hard drives can store files of various formats, but are heavy and cumbersome to take along.

Several manufacturers are hoping to combine the best of both products with small, portable do-it-all devices that not only store and play back music and videos, but which can also serve as a portable hard drive for transferring or backing up data.

"They are rugged, powerful, and portable," says Pierre Maielli, a director at Thomson, a French firm that has created a mobile do-it-all player dubbed the Lyra PDP 2860. Another manufacturer, Archos, is calling its series of similar devices the Video AV 300. Creative, another competing firm, has announced that it will release its Zen Portable Media Centre in autumn. — DPA

"Ageing gene"

Belgian researchers have shed more light on the theory that ageing is associated with a shortening of chromosomes in non-reproductive cells.

Results of the study suggest that the gene responsible for telomere shortening is inherited via the X chromosome. Previous research has shown that the relative length of the ends of chromosomes (telomers) is associated with age-related illness and mortality (shorter telomeres being associated with increased age-related illness and earlier death).

Furthermore, on the basis of studies among twins, telomere length seems to be inheritable, but little is known about its mode of inheritance. — DPA
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